In one type of welding, two or more pieces of metal are heated to their melting points and fused together. Optionally, additional molten metal may be added from a welding filler metal (also sometimes termed “weld rod” or “weld wire” in the art). In another type of welding, the filler metal is melted and applied to a face of a substrate to build up the substrate. This second type of welding is used to repair substrates that have become thinned or damaged during service, or to apply a special facing to the substrate such as a hard facing or an environmentally resistant buildup. In either type of welding, the welding filler metal is melted and fed into the melted region. “Welding filler metal” may be of discrete lengths, which are typically used in manual welding operations, or it may be of continuous lengths used in automated welding machines.
A wide variety of methods are used to manufacture welding filler metal, with drawing or rolling being favored for ductile metals such as steels. The methods that may be used to manufacture welding filler metal of nickel-base superalloys are limited by the inability of most superalloys to be drawn, rolled, or swaged. Powder techniques are also of limited use, as they are expensive and may lead to a final product of insufficient ductility to be useful.
Instead, in conventional commercial practice the nickel-base superalloy to be made into a welding filler metal is cast into a rod about 1 inch in diameter. A number of these rods are sealed into an extrusion can and thereafter extruded to about ¼-inch diameter. The ¼-inch diameter rods are de-canned, cut to length, sealed into another extrusion can, and extruded a second time to about 0.06 inch diameter. This approach is acceptable technically, but it leads to a high cost of the superalloy welding filler metal. About 30 percent or more of the length of each extrusion is lost due to front-end and tail-end extrusion loss, so that the yield of usable welding filler metal from the double-extrusion process is typically less than 50 percent, and often about 25 percent or less, of the weight of the starting material. As a result, the cost of superalloy welding filler metal is sometimes as much as $700 per pound.
There is a need for an improved approach to the manufacture of an acceptable quality, economically produced welding filler metal of nickel-base alloys such as nickel-base superalloys. The present invention fulfills this need, and further provides related advantages.